1. Field of the Invention
The invention relates to a device for adjusting the illumination dose on a photosensitive layer, which is applied to a support that can be displaced in a microlithographic projection exposure apparatus in a scanning direction relative to a projection lens of the projection exposure apparatus. The invention further relates to a method for the microlithographic production of microstructured components.
2. Description of Related Art
Microlithographic projection exposure apparatus, such as those which are used for the production of large-scale integrated electrical circuits, comprise an illumination system for the generation of a projection light beam, a projection lens, a reticle stage for displacing a reticle and a wafer stage for displacing a substrate. The substrate supports a photosensitive layer that is to be chemically modified under the effect of projection light. The reticle and the wafer stage are arranged with respect to the projection lens so that the reticle lies in an object plane and the substrate lies in an image plane of the projection lens. During the projection operation, the projection light passes through the reticle. The projection light then enters the projection lens that images the reticle onto the photosensitive layer.
In such projection exposure apparatus, the projection is often carried out in a scanning operation. This means that the reticle is moved progressively below a narrow slit-shaped light field with the aid of the reticle stage, while the substrate is displaced with the aid of the wafer stage relative to the projection lens. The ratio of the rates of displacement corresponds to the magnification of the projection lens which is usually<1.
In order to establish the slit-shaped light field, use is generally made of stops having a plurality of blades, which are arranged in or close to a field plane of the illumination system and are also referred to as REMA masks (REMA=“REticle MAsking”). A lens in the illumination system comprising several lens elements projects the field plane onto the object plane of the projection lens, where the reticle is to be displaced.
Since exposure of the photosensitive material does not occur until a predetermined illumination dose is exceeded, it is necessary to ensure that all exposed regions on the substrate receive the same illumination dose. Inhomogeneities of the illumination dose can lead to variations in the structure width, since the position of the edges of the structures being produced by the projection exposure apparatus depends on whether or not the necessary illumination dose for exposing the photosensitive layer has been reached.
U.S. Pat. No. 6,404,499 A discloses a corrective device which can improve the homogeneity of the illumination dose. This known device has two mutually opposing arrangements of opaque finger-like stop elements, which are adjacent one another and aligned parallel with the scanning direction. Each pair of mutually opposing stop elements can be displaced in the scanning direction, so that the distance between the mutually opposing ends of the stop elements is variable. In this way, it is possible to establish a slit-shaped light field whose width along the scan direction varies along the longitudinal direction of the slit. Since integration of the light intensity occurs along the scanning direction because of the scanning movement, but not perpendicularly to it, the illumination dose can be defined, by moving the stop elements, for each longitudinal position of the slit-shaped light field.
U.S. Pat. No. 6,081,319 A discloses an illumination system having a gradation filter for obtaining inclined slopes in the irradiance distribution along the scan direction.